Quasi-static axial compressive properties and energy absorption of star-triangular auxetic honeycomb

To systematically and comprehensively investigate the in-plane compression behavior of star-triangular honeycomb (STH) under quasi-static load, a group of specimens were fabricated by additive manufacturing technology and a compression test was carried out. The results show that the deformation of STH is stable, and negative Poisson's ratio (NPR) effect is obvious in the 1-direction. However, this effect is weakened in the 2-direction. Subsequently, numerical simulation models were established to understand the small and large deformation behaviors of STH in detail. In accordance with the deformation mechanism of STH in different directions, theoretical analysis models were developed to predict their elastic modulus and Poisson's ratio, and the results were highly consistent with the numerical simulation results. Detailed parameter analysis shows that the influence of inclined angle theta on the elastic modulus and Poisson's ratio of STH is more obvious than that of t/l. Additionally, with the increase in the inclined angle, the deformation of STH has no obvious difference in the 1-direction while it is considerably different in the 2-direction. When the strain is small, the plateau stress of STH with the same cell-wall angle alpha is similar in different directions. Then, the value of plateau stress and duration of the plateau stage varies greatly with the increase of compression strain. Finally, the energy absorption capacity of STH in different directions was compared. The results show that the energy absorption capacity of STH in the 2-direction is much higher than that in the 1-direction. Furthermore, two energy absorbing stages appear in the compression process of STH, among which the energy contribution of the second stage occupies the largest proportion. This study aims to provide guidelines for the engineering application of STH.